1. Field of the Invention
The present invention relates to a condenser microphone unit.
2. Description of the Related Art
A conventional condenser microphone is provided with a condenser microphone unit having a diaphragm assembly 100 in which a diaphragm 12 is stretched taut over a metal diaphragm support 13A to have predetermined tension, a fixed electrode 20, and a spacer ring (spacer) 30, as shown in FIG. 7.
Further, in the above-mentioned condenser microphone unit, the diaphragm 12 of the diaphragm assembly 100 and the fixed electrode 20 are arranged to face each other through the spacer ring 30.
Furthermore, a support ring formed in a ring shape is used for the above-mentioned diaphragm support 13A. In a situation where predetermined tension is applied to the diaphragm 12, its circumferential edge is adhered to the above-mentioned support ring by means of an adhesive.
As for the diaphragm 12 adhered to the diaphragm support 13A as described above, an area inside the diaphragm support 13A is arranged to operate as an effective vibrating portion (between itself and the fixed electrode 20, it acts as an effective electrostatic-capacitance portion).
Incidentally, the above-mentioned condenser microphone has a structure with which high sensitivity is obtained by increasing (raising) a polarization voltage between the diaphragm 12 and the fixed electrode 20.
However, electrostatic attraction (electrostatic attraction which increases with increasing polarization voltage) takes place between the diaphragm 12 and the fixed electrode 20. Therefore, there arises a problem in that, as shown in FIG. 8, if a voltage greater than a predetermined polarization voltage is applied across the diaphragm 12 and the fixed electrode 20, the diaphragm 12 is pulled by the electrostatic attraction toward the fixed electrode 20 side and then brought into contact therewith, so that the condenser microphone stops operating. In particular, a central part of the diaphragm 12 with weak tension is pulled towards the fixed electrode 20 side and comes into contact therewith. In addition, for convenience of description, the spacer ring 30 is not shown in FIG. 8.
Japanese Patent Application Publication No. 2006-60370 (patent document 1) proposes a structure of the condenser microphone unit which solves the above-mentioned problem.
In particular, the condenser microphone unit of patent document 1 is arranged such that a diaphragm support 13B which stretches the diaphragm 12 tightly is provided with a plurality of openings 13B1 as shown in FIG. 9 to thereby increase vibration tension of the diaphragm 12.
However, even if the plurality of openings 13B1 are provided for the diaphragm support 13B to increase the vibration tension of the diaphragm 12 as in patent document 1 above, the diaphragm 12 cannot sufficiently counter the electrostatic attraction generated in the condenser microphone which has narrow directivity and needs high sensitivity, is attracted by the fixed electrode 20, and may come into contact therewith (see FIG. 10).
In addition, since the polarization voltage is around 600V in the condenser microphone with narrow directivity using a sound tube, the above-mentioned electrostatic attraction is large.
In other words, the condenser microphone unit disclosed in patent document 1 has a technical problem in that when it is used for the condenser microphone with narrow directivity and high polarization voltage, the central part (central part where tension is small) of the diaphragm 12 is pulled by electrostatic attraction toward the fixed electrode 20 side and may come into contact therewith (attach thereto).